Clamp based lesion formation apparatus with variable spacing structures

ABSTRACT

Apparatus including includes first and second energy transmission surfaces with a predetermined spacing and a device that allows the spacing to increase when the energy transmission surfaces are brought into contact with a tissue structure that is thicker than the predetermined spacing.

BACKGROUND OF THE INVENTIONS

1. Field of Inventions

The present inventions relate generally to devices for performingtherapeutic operations on body tissue.

2. Description of the Related Art

There are many instances where electrosurgical devices are used to formtherapeutic lesions in tissue. Therapeutic lesions are frequently formedto treat conditions in the heart, prostate, liver, brain, gall bladder,uterus, breasts, lungs and other solid organs. Electromagnetic radiofrequency (“RF”) may, for example, be used to heat and eventually kill(i.e. “ablate”) tissue to form a lesion. During the ablation of softtissue (i.e. tissue other than blood, bone and connective tissue),tissue coagulation occurs and it is the coagulation that kills thetissue. Thus, references to the ablation of soft tissue are necessarilyreferences to soft tissue coagulation. “Tissue coagulation” is theprocess of cross-linking proteins in tissue to cause the tissue to jell.In soft tissue, it is the fluid within the tissue cell membranes thatjells to kill the cells, thereby killing the tissue. The tissuecoagulation energy is typically supplied and controlled by anelectrosurgical unit (“ESU”) during the therapeutic procedure. Morespecifically, after an electrosurgical device has been connected to theESU, and the electrodes or other energy transmission elements on thedevice have been positioned adjacent to the target tissue, energy fromthe ESU is transmitted through the energy transmission elements to thetissue to from a lesion. The amount of power required to coagulatetissue ranges from 5 to 150 W.

Clamps that carry electrodes or other energy transmission elements onopposable clamp members are used in a wide variety of electrophysiologyprocedures, especially those in which the physician intends to positionelectrodes on opposite sides of a body structure. Examples of clampbased devices which carry energy transmission elements are disclosed inU.S. Pat. No. 6,142,994, and U.S. Patent Pub. No. 2003/0158547 A1, whichare incorporated herein by reference. In a typical clamp basedprocedure, a clamp will be used by the physician to position energytransmission surfaces (such as the outer surface of the exposed portionof the energy transmission elements) on opposite sides of a tissuestructure. Energy may then be transmitted through the tissue from oneenergy transmission surface to the other, which is commonly referred toas bipolar energy transmission, or from each of the energy transmissionsurfaces to an indifferent electrode positioned at a remote locationsuch as the patient's skin, which is commonly referred to as unipolarenergy transmission.

Surgical probes are another example of devices that may be used inelectrophysiology procedures. Surgical probes used to create lesionsoften include a handle, a relatively short shaft that is from 4 inchesto 18 inches in length and either rigid or relatively stiff, and adistal section that is from 1 inch to 10 inches in length and eithermalleable or somewhat flexible. One or more coagulation electrodes orother energy transmission devices are carried by the distal section.Surgical probes are used in epicardial and endocardial procedures,including open heart procedures and minimally invasive procedures whereaccess to the heart is obtained via a thoracotomy, thoracostomy ormedian sternotomy. Exemplary surgical probes are disclosed in U.S. Pat.No. 6,142,994.

Tissue contact is an important issue in any electrophysiology procedure.With respect to clamp based procedures, for example, the failure toachieve and maintain intimate contact between the tissue and energytransmission surfaces can result in gaps in what were intended to becontinuous linear or curvilinear lesions. With respect to the formationof therapeutic lesions in the heart to treat cardiac conditions such asatrial fibrillation, atrial flutter and arrhythmia, such gaps may resultin a failure to cure the arrhythmia and atrial flutter or may createatrial flutter. Moreover, atrial flutter created by gaps in linearlesions can difficult to cure. Poor contact between the tissue andenergy transmission surfaces can also result in lesions that are nottransmural. Lesions which are not transmural may, in turn, fail to curethe patient's arrhythmia or other medical condition.

One method of insuring the proper level of contact in clamp basedelectrophysiology procedures is to configure the clamp in such a mannerthat there is a predetermined (i.e. preset) spacing between the energytransmission surfaces when the clamp is in the closed orientation thatcorresponds to the thickness of the target tissue structure. In additionto insuring intimate tissue contact, the preset spacing also preventsthe mechanical damage to tissue (e.g. cutting through the tissuestructure) that can occur when the spacing between the energytransmission surfaces is less than the thickness of the target tissuestructure when the clamp is closed. For example, electrophysiologyclamps that are intended to position energy transmission surfaces onopposite sides of the tissue around the pulmonary veins have a closedorientation spacing of about 2 mm between the energy transmissionsurfaces.

The present inventors have determined that conventional clamp basedelectrophysiology devices are susceptible to improvement. Morespecifically, the present inventors have determined that there areprocedures where a physician may wish to form lesions in tissuestructures with different thicknesses. The use of a conventional clampbased electrophysiology device with a preset spacing between the energytransmission surfaces can hamper such procedures because a presetspacing that is large enough to accommodate the larger tissue structuresmay be too large to facilitate intimate tissue contact with the smallertissue structures. As such, the use of a single conventional clamp basedelectrophysiology device in procedures that involve tissue structures ofvarying thickness may result in mechanical damage to tissue and/orlesions that are not continuous or transmural.

Another important issue in electrophysiology procedures is energytransmission and, more specifically, the electrical resistivity on thestructure that is in contact with tissue. In some clamp and surgicalprobe based electrophysiology devices that include electrodes, theexposed portions of the electrodes are covered with porous, wettablestructures that are configured to be saturated with and retain ionicfluid (such as saline) prior to use. Tissue coagulation energy may betransmitted to (or to and from) the electrodes by way of the ionicfluid. The present inventors have determined that conventional porous,wettable structures are susceptible to improvement and, in particular,that the electrical resistance across the porous, wettable structuresshould be reduced.

Still another important issue in electrophysiology procedures isconfirming whether a therapeutic lesion has been properly formed duringsurgical procedures. Some clamp and surgical probe basedelectrophysiology devices employ stimulation electrodes that may beplaced on tissue on one side of a lesion, or stimulation and sensingelectrodes that may be placed on tissue on opposite sides of a lesion,and used to confirm whether a therapeutic lesion has been formed duringsurgical procedures. The present inventors have determined that suchclamp and surgical probe based electrophysiology devices are susceptibleto improvement.

SUMMARY OF SOME OF THE INVENTIONS

An apparatus for use with a clamp in accordance with one inventionherein includes first and second energy transmission surfaces with apredetermined spacing when the clamp is closed and a device that allowsthe spacing to increase when the energy transmission surfaces arebrought into contact with a tissue structure that is thicker than thepredetermined spacing. Similarly, a clamp in accordance with oneinvention herein includes first and second energy transmission surfaceswith a predetermined spacing when the clamp is closed and a device thatallows the spacing to increase when the energy transmission surfaces arebrought into contact with a tissue structure that is thicker than thepredetermined spacing. Such devices provide a number of advantages. Forexample, such devices may be used to achieve and maintain intimatecontact between the tissue and energy transmission surfaces, but willnot damage tissue, when brought into contact with the tissue surfacesstructures of varying thickness.

An apparatus for use with an energy transmission element in accordancewith one invention herein includes a wettable structure configured to besaturated with and retain ionic fluid and a plurality of conductivefibers carried by the wettable structure. Such an apparatus provides anumber of advantages. For example, the use of conductive fibers greatlyincreases the conductivity of the apparatus, as compared to an otherwiseidentical wettable structure saturated with the same ionic fluid.

An apparatus in accordance with one invention herein includes a tissuecoagulation device that creates a current path and a stimulationelectrode carried within the current path. Such an apparatus provides anumber of advantages. For example, the apparatus allows the physician toquickly and easily confirm tissue contact, form a lesion, and evaluatethe lesion with the same apparatus and without moving the apparatus. Thelocation of the stimulation electrode also results in more accurateinformation concerning the lesion, as compared to conventionalapparatus, because the assessment of the lesion is localized (i.e. theassessment is made directly on the target tissue within the currentpath).

The above described and many other features and attendant advantages ofthe present inventions will become apparent as the inventions becomebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Detailed description of preferred embodiments of the inventions will bemade with reference to the accompanying drawings.

FIG. 1 is a perspective view of a surgical system in accordance with oneembodiment of a present invention.

FIG. 2 is a section view taken along line 2-2 in FIG. 1.

FIG. 3 is a plan view of a clamp in accordance with a preferredembodiment of a present invention.

FIG. 4 is a section view taken along line 4-4 in FIG. 3.

FIG. 5 is a top view of a portion of the clamp illustrated in FIG. 3.

FIG. 6 is a plan view of a portion of a tissue coagulation assembly inaccordance with one embodiment of a present invention.

FIG. 7 is a side, partial section view of a portion of the tissuecoagulation assembly illustrated in FIG. 6.

FIG. 8 is a side, partial section view of a portion of the tissuecoagulation assembly illustrated in FIG. 6.

FIG. 9 is a section view taken along line 9-9 in FIG. 7.

FIG. 10 is a section view taken along line 10-10 in FIG. 8.

FIG. 11 is a side, partial section view of a portion of theelectrophysiology clamp apparatus illustrated in FIG. 1 in the closedorientation.

FIG. 12 is a side, partial section view of a portion of theelectrophysiology clamp apparatus illustrated in FIG. 1 in the closedorientation engaging a tissue structure.

FIG. 13 is a side, partial section view of a portion of theelectrophysiology clamp apparatus illustrated in FIG. 1 in the closedorientation engaging a tissue structure.

FIG. 14 is a side, partial section view of a portion of theelectrophysiology clamp apparatus in accordance with one embodiment of apresent invention in the closed orientation.

FIG. 15 is a side, partial section view of the portion of theelectrophysiology clamp apparatus illustrated in FIG. 14 engaging atissue structure.

FIG. 16 is a side view of a portion of a modified version of theelectrophysiology clamp apparatus illustrated in FIGS. 14 and 15.

FIG. 17A is a section view of an energy transmission device inaccordance with one embodiment of a present invention.

FIG. 17B is a section view of an energy transmission device inaccordance with one embodiment of a present invention.

FIG. 18A is a side view illustrating a step in a process in accordancewith one embodiment of a present invention.

FIG. 18B is a top view illustrating a step in a process in accordancewith one embodiment of a present invention.

FIG. 18C is a top view of a wettable structures with conductive fibersin accordance with one embodiment of a present invention.

FIG. 18D is a section view taken along line 18D-18D in FIG. 18C.

FIG. 19 is a plan view of a surgical probe in accordance with oneembodiment of a present invention.

FIG. 20 is plan, partial section view of the distal portion of thesurgical probe illustrated in FIG. 19.

FIG. 21 is a section view taken along line 21-21 in FIG. 20.

FIG. 22 is a section view taken along line 22-22 in FIG. 20.

FIG. 23 is a section view taken along line 23-23 in FIG. 20.

FIG. 24 is an end view of the surgical probe illustrated in FIG. 19.

FIG. 25 is a perspective view of a surgical system in accordance withone embodiment of a present invention.

FIG. 26 is a side, partial section view of a tissue coagulation assemblyin accordance with one embodiment of a present invention.

FIG. 27 is a perspective view of a surgical system in accordance withone embodiment of a present invention.

FIG. 28 is a section view taken along line 28-28 in FIG. 27.

FIG. 29 is a plan view of a portion of the tissue coagulation assemblyillustrated in FIG. 26.

FIG. 30 is a plan view of a portion of the tissue coagulation assemblyillustrated in FIG. 26.

FIGS. 31 and 32 are end views showing portions of a lesion formationprocess in accordance with one embodiment of a present invention.

FIG. 33 is a perspective view of a surgical system in accordance withone embodiment of a present invention.

FIG. 34 is an end view of the surgical probe illustrated in FIG. 33.

FIG. 35 is a side, partial section view of a portion of the surgicalprobe illustrated in FIG. 33.

FIG. 36 is a section view taken along line 36-36 in FIG. 35.

FIG. 37 is a section view of a portion of a lesion formation process inaccordance with one embodiment of a present invention.

FIG. 38 is a section view of a portion of a lesion formation process inaccordance with one embodiment of a present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a detailed description of the best presently knownmodes of carrying out the inventions. This description is not to betaken in a limiting sense, but is made merely for the purpose ofillustrating the general principles of the inventions.

The detailed description of the preferred embodiments is organized asfollows:

I. Introduction

II. Exemplary Surgical Systems

Ill. Exemplary Wettable Structures With Conductive Fibers

IV. Power Control

V. Stimulation Electrodes and Lesion Confirmation

The section titles and overall organization of the present detaileddescription are for the purpose of convenience only and are not intendedto limit the present inventions.

I. Introduction

This specification discloses a number of structures, mainly in thecontext of cardiac treatment, because the structures are well suited foruse with myocardial tissue. Nevertheless, it should be appreciated thatthe structures are applicable for use in therapies involving other typesof soft tissue. For example, various aspects of the present inventionshave applications in procedures concerning other regions of the bodysuch as the prostate, liver, brain, gall bladder, uterus, breasts,lungs, and other solid organs.

II. Exemplary Surgical Systems

As illustrated for example in FIG. 1, an exemplary surgical system 10 inaccordance with one embodiment of a present invention includes anelectrophysiology clamp apparatus 100 and an ESU 300. The ESU 300, whichis discussed in Section IV below, supplies and controls power to theelectrophysiology clamp apparatus 100. The electrophysiology clampapparatus 100 includes a clamp and a tissue coagulation assembly thatmay be secured to the clamp. As used herein, the term “clamp” includes,but is not limited to, clamps, clips, forceps, hemostats, and any othersurgical device that includes a pair of opposable clamp members thathold tissue, at least one of which is movable relative to the other. Insome instances, the clamp members are connected to a scissors-likearrangement including a pair of handle supporting arms that arepivotably connected to one another. The clamp members are secured to oneend of the arms and the handles are secured to the other end. Certainclamps that are particularly useful in minimally invasive proceduresalso include a pair of handles and a pair of clamp members. Here,however, the clamp members and handles are not mounted on the oppositeends of the same arm. Instead, the handles are carried by one end of anelongate housing and the clamp members are carried by the other. Asuitable mechanical linkage located within the housing causes the clampmembers to move relative to one another in response to movement of thehandles. The clamp members may be linear or have a predefined curvaturethat is optimized for a particular surgical procedure or portionthereof. The clamp members may also be rigid or malleable.

One example of a clamp is generally represented by reference numeral 102in FIGS. 1 and 3-5. Referring more specifically to FIGS. 3-5, the clamp102 includes a pair of rigid arms 104 and 106 that are pivotablyconnected to one another by a pin 108. The proximal ends of the arms 104and 106 are respectively connected to a pair handle members 110 and 112,while the distal ends are respectively connected to a pair of clampmembers 114 and 116. The clamp members 114 and 116 may be rigid ormalleable and, if rigid, may be linear or have a pre-shaped curvature. Alocking device 118 locks the clamp in the closed orientation, andprevents the clamp members 114 and 116 from coming any closer to oneanother than is illustrated in FIGS. 3 and 11-13, thereby defining apredetermined (or preset) spacing between the clamp members. The clamp102 is also configured for use with a pair of soft, deformable inserts(not shown) that may be removably carried by the clamp members 114 and116 and allow the clamp to firmly grip a bodily structure withoutdamaging the structure. To that end, the clamp members 114 and 116 eachinclude a slot 120 (FIGS. 4 and 5) that is provided with a sloped inletarea 122 and the inserts include mating structures that are removablyfriction fit within the slots. The present tissue coagulation andstimulation assemblies may be mounted on the clamp members in place ofthe inserts.

With respect to the tissue coagulation assembly, the tissue coagulationassembly 124 in the exemplary electrophysiology clamp apparatus 100illustrated in FIG. 1 includes a first energy transmission device 126that may be connected to one of the clamp members 114 and 116 and asecond energy transmission device 128 that may be connected to theother. The energy transmission devices 126 and 128 are respectivelycarried on support structures 130 and 132, which are connected to acable 134 by a molded junction 136. The other end of the cable 134enters a handle 138. The support structures 130 and 132 in theillustrated embodiment are flexible tubular structures which have anouter diameter that is, depending on the diameter of the electrodes 140,142 and 144 (discussed below), typically between about 1.5 mm and about3 mm. The support structures 130 and 132 in the illustrated embodiment,which are intended for use in cardiovascular applications, have an outerdiameter of about 2 mm. Suitable support structure materials include,for example, flexible biocompatible thermoplastic tubing such asunbraided Pebax® material, polyethylene, or polyurethane tubing.

Although tissue coagulation assemblies in accordance with the presentinventions may be operated in bipolar and unipolar modes, the exemplarytissue coagulation assembly 124 is configured so as to be especiallyuseful in a bipolar mode wherein the first energy transmission device126 will transmit energy through tissue to the second energytransmission device 128. To that end, and as illustrated for example inFIGS. 7 and 8, the first energy transmission device 126 includes a pairof electrodes 140 and 142 that may be independently controlled, whilethe second energy transmission device 128 includes a single electrode144. Such an arrangement provides for higher fidelity control of theoverall region that is transmitting energy and a gap free, constantpotential region on the return side.

The spaced electrodes 140, 142 and 144 are preferably in the form ofwound, spiral closed coils. The coils are made of electricallyconducting material, like copper alloy, platinum, or stainless steel, orcompositions such as drawn-filled tubing (e.g. a copper core with aplatinum jacket). The electrically conducting material of the coils canbe further coated with platinum-iridium or gold to improve itsconduction properties and biocompatibility. Preferred coil electrodesare disclosed in U.S. Pat. Nos. 5,797,905 and 6,245,068.

Alternatively, the electrodes 140, 142 and 144 may be in the form ofsolid rings of conductive material, like platinum, or can comprise aconductive material, like platinum-iridium or gold, coated upon thedevice using conventional coating techniques or an ion beam assisteddeposition (IBAD) process. For better adherence, an undercoating ofnickel, silver or titanium can be applied. The electrodes can also be inthe form of helical ribbons. The electrodes can also be formed with aconductive ink compound that is pad printed onto a non-conductivetubular body. A preferred conductive ink compound is a silver-basedflexible adhesive conductive ink (polyurethane binder), however othermetal-based adhesive conductive inks such as platinum-based, gold-based,copper-based, etc., may also be used to form electrodes. Such inks aremore flexible than epoxy-based inks. Open coil electrodes may also beemployed. Still other types of electrodes are formed from electrolessplated copper on a polyimide film or tubular substrate. Gold, nickel orsilver should be plated over the copper for electrochemical stabilityand improved biocompatibility. The plating can be applied in continuousform (up to about 1-2 cm in length at most) or can be applied in apattern that is designed to improve current density distributions and/orelectrode flexing characteristics. Temperature sensors (e.g.thermocouples) may be incorporated into the electrode structure byplacing the temperature sensors in a channel in the polyimide film ortubular substrate and then plating over them.

The electrodes 140 and 142 are preferably about 1.5 cm to 4 cm in lengthwith about 1 mm to 3 mm spacing, which will result in the creation ofcontinuous lesion patterns in tissue when coagulation energy is appliedsimultaneously to adjacent electrodes. The length of the electrode 144is preferably the combined length of the electrodes 140 and 142,including the spacing therebetween, so that the overall electrode lengthon the first and second energy transmission devices 126 and 128 is thesame.

The first and second energy transmission devices 126 and 128 in theembodiment illustrated in FIGS. 1 and 6-13 are also provided withrespective mounting devices 146 that may be used to mount the tissuecoagulation assembly 124 in general, and the energy transmission devicesin particular, on the clamp 102. Additionally, although theconfiguration of the tissue coagulation assembly 124 may vary fromapplication to application to suit particular situations, the exemplarytissue coagulation assembly is configured such that the electrodes 140and 142 will be parallel to the electrode 144 when the clamp 102 is inthe closed orientation.

Referring more specifically to FIGS. 7-10, the mounting devices 146 areidentical in the illustrated embodiment. Each mounting device 146includes a base member 148 that has a groove 150 which is configured toreceive the support structure 130 and electrodes 140 and 142 (or supportstructure 132 and electrode 144). About 20% of the electrode surface(i.e. about 75° of the 360° circumference) is exposed in the illustratedembodiment. Adhesive may be used to hold the support structures andelectrodes in place. The mounting device also includes a connector 152that is configured to removably mate with the clamp slot 120 (FIGS. 4and 5). The exemplary connector 152 is provided with a relatively thinportion 154 and a relatively wide portion 156, which may consist of aplurality of spaced members (as shown) or an elongate unitary structure,in order to correspond to the shape of the slot 120.

The mounting devices 146 are preferably formed from polyurethane. Thelength of the mounting devices 146 will vary according to the intendedapplication. In the area of cardiovascular treatments, it is anticipatedthat suitable lengths will range from, but are not limited to, about 4cm to about 10 cm. In the exemplary implementation, the mounting devices146 are about 7 cm in length.

The electrodes 140 and 142 in the exemplary tissue coagulation assembly124 are connected to power wires 158, while the electrode 144 isconnected to a power wire 160, as shown in FIGS. 9 and 10. The powerwires 158 and 160 extend through the support structures 130 and 132,respectively, as well as the cable 134, and into the handle 138. Thepower wires 158 extend into a cable 162 (FIG. 1) with a power connector164 that extends proximally from the handle 136, while the power wire160 extends into a cable 166 with a return connector 168 that alsoextends proximally from the handle.

A plurality of temperature sensors 170 (FIG. 9), such as thermocouplesor thermistors, may be located on, under, abutting the longitudinal endedges of, or in between, the electrodes 140 and 142. A referencethermocouple (not shown) may also be provided. In the exemplaryimplementation, temperature sensors 170 are located at both longitudinalends of each of the electrodes 140 and 142. The temperature sensors 170are connected to signal wires 172, which pass through the supportstructure 130, cable 134 and cable 162. The temperature sensors 170 arealso located within a linear channel 174 that is formed in the supportstructure 130. The linear channel insures that the temperature sensorswill all face in the same direction (e.g. facing tissue) and be arrangedin linear fashion.

The energy transmission devices 126 and 128 also include variablespacing structures 176, as is shown in FIGS. 1 and 6-13. The variablespacing structures 176, which are substantially identical in theillustrated embodiment and each define an energy transmission surface178, allow the energy transmission devices 126 and 128 to achieveintimate tissue contact with tissue structures of varying thicknesswithout mechanically damaging the thicker structures. Referring morespecifically to FIGS. 11 and 12, the exemplary clamp apparatus 100 isconfigured such that there is a preset spacing CS between the clampmembers 114 and 116 when the clamp 102 is in the completely closedorientation. The energy transmission devices 126 and 128 and variablespacing structures 176 are correspondingly configured such that there isa preset spacing S₁ between the energy transmission surfaces 178 whenthe clamp 102 is in the closed orientation illustrated in FIG. 11. Whenthe clamp apparatus 100 is closed on opposite sides of a tissuestructure T that is thicker than the spacing S₁, the variable spacingstructures 176 will compress, and the spacing between the energytransmission surfaces 178 will increase to S₂ as shown in FIG. 12, inorder to accommodate the tissue structure. The spacing CS between theclamp members 114 and 116 will, however, remain the same. The variablespacing structures 176 are preferably configured such that as theycompress from the state illustrated in FIG. 11 to the state illustratedin FIG. 12, there will not be a significant increase in the clampingforce applied to a tissue structure therebetween.

Another advantage associated with the variable spacing structures 176 isassociated with tissue contact at the edge of a tissue structure. Asillustrated in FIG. 13, the resiliency of the variable spacingstructures 176 allows the energy transmission surfaces 178 to wraparound the tissue structure edge TE, thereby providing better contactalong the edge than could be achieved with a more rigid energytransmitting structure that would not wrap around the edge. Bettercontact results in better lesions and reduces the likelihood that therewill be gaps in a lesion at the edge of a tissue structure.

In implementations intended for use in the treatment of cardiacconditions such as atrial fibrillation, for example, the spacing S₁between the energy transmission surfaces 178 may be about 1 mm and thespacing S₂ may be about 2 mm. As such, the energy transmission devices126 and 128 will achieve and maintain intimate contact between thetissue and energy transmission surfaces 178 when brought into contactwith the epicardial and endocardial surfaces that are about 1 mm apart(typically by inserting one of the energy transmission through a cut inthe left atrial wall), but will not damage tissue when positioned onopposite sides of the tissue around the pulmonary veins, which is about2 mm thick after the opposite sides are brought together.

Although the present inventions are not limited to any particularinstrumentality for facilitating the increase in spacing when a targettissue structure is thicker than the preset spacing S₁, the exemplaryvariable spacing structures 176 include a resilient member 180 and abarrier member 182. Referring to FIGS. 11-13, the resilient members 180in the exemplary implementation are configured to compress in the mannerdescribed above, thereby acting as cushions for tissue structures thatare thicker than the preset spacing S₁. The resilient members 180 arealso porous, wettable structures that are configured to be saturatedwith and retain ionic fluid (such as saline) prior to use so that energymay be transmitted to and from the associated electrodes by way of theionic fluid. Suitable materials include foams, such as open cell foams,reticulated foams, non-reticulated foams, fine cell foams andhydrocolloide foams. Other suitable materials include hydrogels, thickwoven biocompatible materials (e.g. Dacron®), cotton and cellulose. Thethickness of the resilient members 180 (i.e. the distance from the outersurface of the associated electrode to the inner surface of theassociated barrier member) may range from about 1 mm to 3 mm and isabout 1.5 mm in the illustrated embodiment.

Turning to the barrier members 182 in the exemplary variable spacingstructures 176, each barrier member is preferably a porous structurethat is used to secure the associated resilient member 180 in place. Tothat end, the side edges 184 of the barrier members 182 are secured tothe mounting device base members 148 (FIG. 10). The barrier members 182,the outer surfaces of which define the energy transmission surfaces 178,are also preferably porous and are hydrophilic so that they may retainthe aforementioned ionic fluid through which energy is transmittedduring electrophysiology procedures. The thickness of the barriermembers 182 may range from about 0.05 mm to 0.5 mm and is about 0.2 mmin the illustrated embodiment.

The barrier members 182 may also be used to perform a number of otherfunctions. For example, the barrier members 182 prevent tissue ingressinto the resilient member 180 during electrophysiology procedures, whichcan result in the tissue sticking to the resilient member and tissuetearing when the energy transmission devices 126 and 128 are moved.Suitable materials for the barrier member 182 include biocompatiblefabrics commonly used for vascular patches (such as woven Dacron®). Onespecific example is Hemashield Finesse™ from Boston ScientificCorporation. Such material may be easily cleaned during anelectrophysiology procedure with alcohol or saline, which furtherfacilitates the formation of multiple lesions with the same tissuecoagulation assembly 124 during a single electrophysiology procedure.

It should be noted that the effective electrical resistivity of eachvariable spacing structure 176 when wetted with 0.9% saline (normalsaline) should range from about 1 Ω-cm to about 2000 Ω-cm. A preferredresistivity for epicardial and endocardial procedures is about 1000Ω-cm, which is much closer to the resistivity of tissue than that of theelectrodes. As a result, energy transmission devices with the variablespacing structure 176 will have lower edge currents and provide moreuniform current distribution than energy transmission device that areconfigured to place the electrodes in direct contact with tissue.

The distal portion of another exemplary clamp apparatus 100 a isillustrated in FIGS. 14 and 15. The clamp apparatus 100 a is essentiallyidentical to the clamp apparatus 100 and similar elements arerepresented by similar reference numerals. The clamp apparatus 100 a is,however, configured such that there is no spacing S₁ between the energytransmission surfaces 178, i.e. the energy transmission surfaces are incontact with one another, when the clamp 102 is in the closedorientation illustrated in FIG. 14. This may be accomplished by slightlymodifying the dimensions of the clamp and/or the energy transmissiondevices. In the illustrated embodiments, the energy transmission devices126 a and 128 a are slightly thicker than the energy transmissiondevices 126 and 128 in the clamp apparatus 100.

When the clamp apparatus 100 a is closed on opposite sides of a tissuestructure, such as the compressed pulmonary vein PV illustrated in FIG.15, the associated portions of the variable spacing structures 176 willcompress, and the spacing between the energy transmission surfaces 178increase to S₂ in order to accommodate the tissue structure. Theportions of the energy transmission surfaces 178 of the clamp apparatus100 a that are not in contact with a tissue structure will remain incontact with one another when other portions are in contact with atissue structure. As a result, there will not be any electricallynon-conductive gaps between the energy transmission surfaces 178.

The configuration illustrated in FIGS. 14 and 15 is advantageous for anumber of reasons. For example, the entire surface of the tissuestructure (e.g. the compressed pulmonary vein PV illustrated in FIG.15), including the lateral edge surfaces, is in contact with a portionan energy transmission surface 178 of a variable spacing structure 176.As noted above, increasing the amount of edge tissue contacted by theenergy transmission surfaces reduces the likelihood that there will begaps in a lesion at the edge of the tissue structure.

Another advantage is associated with the portions of the energytransmission surfaces 178, and the underlying electrodes, that are notin contact with tissue. As discussed in Section IV below, power to thetransmitting electrodes 140 and 142 may be controlled by the ESU 300(FIG. 1) on an electrode-by-electrode basis. In some instances, thetissue coagulation procedure will be shut down when there is no currentpath from one of the transmitting electrodes 140 and 142 to the returnelectrode 144. In the exemplary implementation illustrated in FIGS. 14and 15, such current paths are insured because the energy transmissionsurfaces 178 are either in contact with tissue or are in contact withone another.

Conversely, as illustrated in FIG. 16, when an otherwise identicalelectrophysiology clamp that lacks the variable spacing structures 176is positioned around a pulmonary vein PV or other tissue structure, itis possible that there will be a gap between one of the transmittingelectrodes 140 and 142 and the return electrode 144. In the illustratedsituation, there is a current path from the transmitting electrode 142to the return electrode 144 (i.e. the pulmonary vein PV), but there isno current path from the transmitting electrode 140 to the returnelectrode due to the gap. This may result in the ESU 300 stopping thecoagulation procedure.

Finally, the clamp and the tissue coagulation assemblies described abovemay be combined into an integral unit that cannot be readily separated.For example, the base members may be molded onto the clamp members. Suchbase members would, for example, extend completely around the each clampmember and/or include portions that are molded into the slots. The basemembers, clamp members, electrodes, etc. could also be formed as aunitary structure using, for example, insert molding techniques.

III. Exemplary Wettable Structures with Conductive Fibers

As noted above, the resilient members 180 are wettable structures thatare configured to be saturated with and retain ionic fluid prior to useso that energy may be transmitted to and from the associated electrodesby way of the ionic fluid. In accordance one of the present inventions,the electrical resistance of such wettable structures may be reduced byadding conductive fibers thereto and, to that end, the resilient members180 b illustrated in FIGS. 17A and 17B include a plurality of conductivefibers 186 in addition to the wettable material. Although the presentinventions are not limited to any particular concentration of conductivefibers 186, the conductive fibers will typically occupy less than 5% ofthe volume of the resilient member 180 b.

Wettable structures with conductive fibers may be used in combinationwith wide variety of devices. By way of example, but not limitation, theresilient members 180 b may be carried on the energy transmissiondevices 126 b and 128 b illustrated in FIGS. 17A and 17B. The energytransmission devices 126 b and 128 b may form part of anelectrophysiology clamp apparatus that is otherwise identical to theelectrophysiology clamp apparatus 100 illustrated in FIG. 1. Anotherexample is the surgical probe 200 described below with reference toFIGS. 19-24.

Although the present inventions are not limited to any particularorientation, the conductive fibers 186 in the illustrated embodiment areparallel to the direction of current flow, which is represented by thearrows CF in FIG. 17A. The current flow direction is generallyperpendicular to a flat energy transmission element and radial from acurved energy transmission element, such as the electrodes 140 and 144in FIGS. 17A and 17B. So arranged, the conductive fibers will beperpendicular to the bottom surface of the wettable material if theresilient member is not curved, or perpendicular to the associatedtangent if the resilient member 180 b is curved or has been bent over acurved energy transmission element (as it has is in FIGS. 17A and 17B).Orienting the conductive fibers 186 parallel to the current flowdirection is considerably more effective from a resistance reductionstandpoint than a random orientation. For comparison purposes,conductive fibers that are perpendicular to the current flow directionhave almost no influence on electrical impedance until the amount offibers approaches 30 percent of the volume of the resilient member.

The length of the conductive fibers 186 and their position relative tothe electrode are other important considerations. Preferably, the lengthof the conductive fibers 186 will be at least one-half of the thicknessof the resilient wettable structure. Conductive fibers that extend tothe bottom surface of the resilient member and are in physical contactwith the underlying electrode (as they are in the illustratedembodiment) will have twice the effect on conductance as compared toconductive fibers that are not in physical contact. Moreover, conductivefibers that are spaced more than about 1 fiber radius from the electrodewill be essentially disconnected from the electrode.

The fractional increase in electrical conductance of a wettablestructure provided with conductive fibers that are parallel to thedirection of current flow may be expressed as:[(2)·(% Fiber)·(T²/D²)]/[−In(% Fiber)]where % Fiber=the volumetric percentage of fiber in the structureexpressed as a decimal (e.g. 1%=0.01), T=the thickness of the wettablestructure, D=the average diameter of the conductive fibers.

For example, if metallic fibers that are 0.1 mm in diameter occupy 1percent of the volume a wettable structure that is 2 mm thick, thefibers would provide an additional conductance of 14-fold compared tothat provided by saline alone (i.e. the resistance would be reduced byabout 15-fold). Similarly, if carbon fibers that are 0.02 mm in diameteroccupy 1 percent of the volume of a wettable structure that is 2 mmthick, the fibers would provide an additional conductance of about300-fold compared to that provided by saline alone. The resistance ofthe overall structure would be less than 1 percent of the resistancewithout the fibers. Even lesser amounts of conductive fibers alsoprovide great benefits. For example, if carbon fibers that are 0.02 mmin diameter occupy 0.1 percent of the volume a wettable structure thatis 2 mm thick, the fibers would provide an additional conductance ofabout 20-fold compared to that provided by saline alone. The resistanceof the overall structure would be about 5 percent of the resistancewithout the fibers. It should also be noted that, in addition to theaforementioned metallic and carbon fibers, fibers formed fromelectrically conductive plastics may also be used.

The resistivity of the conductive fibers 186 is much lower than theresistivity of ionic fluid (such as saline) and, accordingly, thespecific conductivity of the fibers has almost no effect on overallsystem resistivity within the resilient material. Carbon fiber has aconductivity more than 10 ⁵ larger than saline, and almost all metalshave conductivities 10⁸ or more higher than saline. However, the ratiosof the conductivities need only be larger than the T²/D² ratio.

One method of manufacturing the wettable resilient member 180 b withconductive fibers 186 is illustrated in FIGS. 18A and 18B. First, theconductive fibers 186 are sewn in place into a thin, elongate strip ofresilient material 187 such as the aforementioned woven biocompatiblematerial. The conductive fibers 186 may, alternatively, be woven intothe strip of resilient material 187. In either case, the conductivefibers 186 are oriented perpendicularly to the longitudinal axis of thestrip of resilient material 187. Next, as illustrated in FIG. 18B, thestrip of resilient material 187 with the conductive fibers 186 isz-folded back and forth over itself and compressed in the direction ofarrow A. This process results in the resilient member 180 b withconductive fibers 186 illustrated in FIGS. 17A, 17B, 18C and 18D.

The surgical probe 200 illustrated in FIGS. 19-24 is another example ofa device that may include a wettable resilient member with conductivefibers. The surgical probe 200 includes a relatively short shaft 202with a proximal section 204, which is connected to a handle 206, and adistal section 208, on which coagulation electrodes 210 (or other energytransmission elements) and a tip member 212 are supported. A strainrelief device 214 may also be provided. The resilient member 180 cillustrated in FIGS. 19, 20 and 23 includes a plurality of conductivefibers 186. The resilient member 180 c, which extends around the distalsection 208 in the manner illustrated in FIG. 23, is essentiallyidentical to the resilient member 180 b, but for the fact that theresilient member 180 c extends completely around the underlyingelectrodes. A barrier member 182 c that extends around the resilientmember 180 c, and is formed from the barrier materials described above,may also be provided if desired.

With respect to the particulars of the exemplary surgical probe 200, theshaft proximal section 204 consists of a hypotube 216, which is eitherrigid or relatively stiff, and an outer polymer tubing 218 over thehypotube. The shaft proximal section 204 in the illustrated embodimentmay be from 4 inches to 18 inches in length and is preferably 6 inchesto 8 inches. The shaft distal section 208, which is preferably eithermalleable, somewhat flexible or some combination thereof, may be from 1inch to 20 inches in length and is preferably 3 to 5 inches. As usedherein the phrase “relatively stiff” means that the shaft (or distalsection or other structural element) is either rigid, malleable, orsomewhat flexible. A rigid shaft cannot be bent. A malleable shaft is ashaft that can be readily bent by the physician to a desired shape,without springing back when released, so that it will remain in thatshape during the surgical procedure. Thus, the stiffness of a malleableshaft must be low enough to allow the shaft to be bent, but high enoughto resist bending when the forces associated with a surgical procedureare applied to the shaft. A somewhat flexible shaft will bend and springback when released. However, the force required to bend the shaft mustbe substantial. Rigid and somewhat flexible shafts are preferably formedfrom stainless steel, while malleable shafts are formed from annealedstainless steel. In those instances where a malleable shaft proximalportion 204 is desired, the hypotube 216 may be a heat treated malleablehypotube. By selectively heat treating certain portions of the hypotube,one section of the hypotube can be made more malleable than the other.The outer tubing 218 may be formed from Pebax® material, polyurethane,or other suitable materials. Additional information concerning“relatively stiff” shafts is provided in U.S. Pat. No. 6,142,994, whichis incorporated herein by reference.

As noted above, the shaft distal section 208 can be either somewhatflexible, in that it will conform to a surface against which it ispressed and then spring back to its original shape when removed from thesurface, malleable, or some combination thereof. In the exemplaryimplementation illustrated in FIGS. 19-24, the distal section 208includes a malleable proximal portion and a flexible distal portion.Although the relative lengths of the portions may vary to suitparticular applications, the malleable proximal portion and a flexibledistal portion are equal in length in the illustrated embodiment.Referring more specifically to FIGS. 20, 22 and 23, the exemplary shaftdistal section 208 includes an outer member 220 that carries theelectrodes 210. The outer member 220 is a flexible tubular structurewhich has an outer diameter that is, depending on the diameter of theelectrodes 210, typically between about 2 mm and about 4 mm. The outermember 220 in the illustrated embodiment, which is intended for use incardiovascular applications, typically has an outer diameter of about 3mm. Suitable support structure materials include, for example, flexiblebiocompatible thermoplastic tubing such as unbraided Pebax® material,polyethylene, or polyurethane tubing.

Turning to the interior of the shaft distal section 208, the exemplarymalleable portion includes a mandrel 222 (FIG. 4) made of a suitablymalleable material, such as annealed stainless steel or berylliumcopper, that may be fixed directly within the distal end of the shaft'shypotube 216 and secured by, for example, soldering, spot welding oradhesives. An insulating sleeve 224, which is preferably formed fromPebax® material, polyurethane, or other suitable materials, is placedover the mandrel 222. With respect to the flexible portion, a springmember 226, which is preferably either a solid flat wire spring (FIG.5), a round wire, or a three leaf flat wire Nitinol® spring, isconnected to the distal end of the mandrel 222 with a crimp tube orother suitable instrumentality. The distal end of the spring member 226is connected to the tip member 212 by, for example, an adhesive orwelding. The tip member 212 is also secured to the distal end of theouter member 220. Other spring members, formed from materials such as17-7 or carpenter's steel, may also be used. The spring member 226 isalso enclosed within the insulating sleeve 224. The spring member 226may be pre-stressed so that the distal tip is pre-bent into a desiredshape. Additional details concerning distal sections that have amalleable proximal portion and a flexible distal portion are provided inU.S. Pat. No. 6,464,700, which is incorporated herein by reference.

In an alternative configuration, the distal section 208 may be formed bya hypotube that is simply a continuation of the shaft hypotube 216covered by a continuation of the outer tubing 218. However, the distalend hypotube can also be a separate element connected to the shafthypotube 216, if it is desired that the distal end hypotube havedifferent stiffness (or bending) properties than the shaft hypotube. Itshould also be noted that the distal section 208 may be made malleablefrom end to end by eliminating the spring member 226 and extending themalleable mandrel 222 to the tip member 212. Conversely, the distalsection 208 may be made flexible from end to end by eliminating themalleable mandrel 222 and extending the spring member 226 from thehypotube 216 to the tip member 212.

The electrodes 210 are preferably wound, spiral closed coils that arepreferably about 4 mm to about 20 mm in length and formed from the samematerials as the electrodes 140, 142 and 144. In the illustratedembodiment, the surgical probe 200 includes seven (7) electrodes 210 andthe electrodes are 12.5 mm in length with 1 mm to 3 mm spacing, whichwill result the creation of continuous lesion patterns in tissue whencoagulation energy is applied simultaneously from adjacent electrodesthrough tissue to an indifferent electrode. The diameter of theelectrodes 210 will typically be about 3 mm. The electrodes 210 may,alternatively, be formed from the other materials and methods discussedabove with reference to the electrodes 140, 142 and 144.

A plurality of temperature sensors 228 (FIG. 23), such as thermocouplesor thermistors, may be located on, under, abutting the longitudinal endedges of, or in between, the electrodes 210. A reference thermocouple(not shown) may also be provided. In the exemplary implementation,temperature sensors 228 are located at both longitudinal ends of each ofthe electrodes 210 within a linear channel 230 that is formed in theouter member 220. The linear channel insures that the temperaturesensors will all face in the same direction (e.g. facing tissue) and bearranged in linear fashion.

The electrodes 210 are connected to power lines 232 and the temperaturesensors 228 are connected to signal lines 234. The power lines 232 maybe used to transmit energy from the power supply and control apparatus300 to the coagulation electrodes 210, while signal lines 234 returntemperature information from the temperature sensors 228 to the powersupply and control apparatus. The power lines 232 and signal lines 234extend from the coagulation electrodes 210 and temperature sensors 228to a connector (such as the exemplary PC board 236 illustrated in FIG.24) that is carried by the handle 206. The handle 206 also includes aport 238 that is configured to receive a suitable connector, such as theconnector 308 from the power supply and control apparatus 300 in theexemplary surgical system 20 illustrated in FIG. 25, for connection tothe PC board 238.

IV. Power Control

As noted above, the exemplary ESU 300 supplies and controls power to thetissue coagulation assembly 124 and the surgical probe 200. A suitableESU is the Model 4810A ESU sold by Boston Scientific Corporation ofNatick, Mass., which is capable of supplying and controlling RF power inboth bipolar and unipolar modes on an electrode-by-electrode basis. Suchelectrode-by-electrode power control is sometimes referred to as“multi-channel control.” Typically, power will be controlled as afunction of the temperature at each electrode in order to insure thattissue is coagulated without over-heating and causing coagulum andcharring. With respect to temperature sensing, temperature at theelectrodes 140 and 142 on the tissue coagulation assembly 124 ismeasured by the aforementioned temperatures sensors 170, whiletemperature at the surgical probe electrodes 210 is measured by thetemperature sensors 228. Alternatively, in those instances wheretemperature sensors are not employed, the respective temperatures at theelectrodes may be determined by measuring impedance at each electrode.

Referring to FIG. 1, the exemplary ESU 300 is provided with a poweroutput connector 302 and a pair of return connectors 304 which arerespectively configured to be connected to the power and returnconnectors 164 and 168 on the tissue coagulation assembly 124. As such,the electrodes 140 and 142 and temperature sensors 170 may be connectedto the ESU power output connector 302, and the electrode 144 may beconnected to the return connector 304. The ESU power output and returnconnectors 302 and 304 may have different shapes to avoid confusion andthe power and return connectors 164 and 168 may be correspondinglyshaped. In the exemplary bipolar tissue coagulation assembly 124illustrated in FIG. 1, for example, the power connector 164 has agenerally circular shape corresponding to the ESU power output connector302 and the return connector 168 has a generally rectangular shapecorresponding to the ESU return connector 304.

Turning to FIG. 25, the surgical system 20 includes the surgical probe200 and the ESU 300. The ESU 300 transmits energy to the electrodes 210and receives signal from the temperature sensors 228 by way of a cable306 and a connector 308, which may be connected to the PC board in thesurgical probe handle 206 in the manner described above. The exemplaryESU 300 is operable in a bipolar mode, where tissue coagulation energyemitted by one of the electrodes 210 is returned through another, and aunipolar mode, where the tissue coagulation energy emitted by theelectrodes is returned through one or more indifferent electrodes 310that are externally attached to the skin of the patient with a patch, orone or more electrodes (not shown) that are positioned in the bloodpool, and a cable 312.

Additional information concerning suitable temperature sensing and RFpower supply and control is disclosed in U.S. Pat. Nos. 5,456,682,5,582,609, 5,755,715 and U.S. Patent Pub. No. 2004/0059325 A1.

V. Stimulation Electrodes and Lesion Confirmation

Electrophysiology devices in accordance with the present inventions mayalso be provided with stimulation electrodes that are used to stimulatetissue (such as by pacing). The stimulation electrodes may be used toperform a variety of functions before, during and after a lesionformation procedure. For example, and as described in greater detailbelow, the stimulation electrodes may be used to confirm tissue contactprior to supplying coagulation energy, to evaluate the lesion as thecoagulation energy is supplied, and to confirm whether or not atherapeutic lesion has been formed after the coagulation energy has beendiscontinued. Stimulation energy may be used because non-viable tissue(e.g. coagulated tissue) cannot be stimulated and will not propagatestimulation energy to nearby tissue.

To that end, the exemplary electrophysiology system 10 c illustrated inFIG. 27 includes an electrophysiology clamp apparatus 100 c, the abovedescribed ESU 300, a tissue stimulation apparatus 350, and an EPrecording apparatus 352. The tissue stimulation apparatus 350 is capableof providing pulses of energy that stimulate (but do not coagulate)tissue. One exemplary tissue stimulation apparatus 350 is a conventionalpacing apparatus, such as the Medtronic Model Nos. 5330 and 5388external pulse generators. The EP recording apparatus 352 is connectedto, and directs the tissue stimulation and recording associated with,the tissue stimulation apparatus 350. A suitable EP recording apparatusis the Prucka CardioLab 7000® from GE Medical Systems. Alternatively,the electrophysiology clamp apparatus 100 c may be directly connected tothe tissue stimulation apparatus 350 or connected to the tissuestimulation apparatus by way of a simple switching box.

It should also be noted that the functionality of the tissue stimulationapparatus 350 may be incorporated into the ESU 300. Here, however, ESUand associated surgical devices should be configured such thatcoagulation electrodes will only receive coagulation energy and thestimulation electrodes will only receive stimulation energy. Here too,this may be accomplished with different connector configurations. Thefunctionality of the tissue stimulation apparatus 350 and the EPrecording apparatus 352 may also be combined into a single device.

With respect to the stimulation energy itself, the power delivered totissue for stimulation purposes will typically be significantly lessthan that which would form a transmural or otherwise therapeutic lesionin tissue. An exemplary stimulation energy delivery would consist of twostimulation pulses per second, each pulse being 1 millisecond. Themaximum amplitude would typical be 10 mA, which would create 0.5 V, fora total power delivery of 10 μW. As noted above, the amount of powerrequired to coagulate tissue ranges from 5 to 150 W. The amplitude maybe increased in those instances where the stimulation pulses are beingsupplied at the same time as the tissue coagulation energy, as isdescribed below.

Turning to the exemplary electrophysiology clamp apparatus 100 c, and asillustrated in FIGS. 26-30, it includes a clamp 102 and a tissuecoagulation assembly 124 c that is essentially identical to the tissuecoagulation assembly 124. Similar elements are used to represent similarelements. Here, however, the first and second energy transmissiondevices 126 c and 128 c are provided with stimulation electrodes 188 and190 in addition to the coagulation electrodes 140-144. The stimulationelectrodes 188 and 190 are carried on the energy transmission surfaces178 of the variable spacing structures 176. Alternatively, thestimulation electrodes 188 and 190 may be located between the resilientmember 180 and a barrier member 182 or, in instances where there is nobarrier member, simply on the exterior of the resilient member. Thestimulation electrodes 188 and 190 may also be used in conjunction withresilient members, such as resilient member 180 a, that includesconductive fibers 186. The stimulation electrodes 188 are connected tosignal wires 192 and the stimulation electrodes 190 are connected tosignal wires 194. The signals wires 192 and 194 are preferablyconfigured such that they will not change the mechanical properties ofthe resilient material. Suitable signal wires include wires that are 38gauge or smaller.

The signal wires 192 traverse the resilient material 180 and enter thesupport structure 130 near the stimulation electrodes 188 (i.e. betweenthe windings of the underlying coagulation electrodes 140 and 142 orbetween the underlying coagulation electrodes) as shown or,alternatively, just proximal to the underlying coagulation electrodes.The signal wires 194 traverse the resilient material 180 and enter thesupport structure 132 near the stimulation electrodes 190 (i.e. betweenthe windings of the underlying coagulation electrode 144) as shown or,alternatively, just proximal to the underlying coagulation electrode.The signal lines 192 and 194, which pass through the cable 134, thehandle 138, and a cable 135, are connected to the EP recording apparatus352 by a connector 137.

Referring to FIGS. 26, 29 and 30, the stimulation electrodes 188 and 190in the exemplary embodiment are positioned such that they are locatedbetween, and aligned with, the tissue coagulation electrodes 140-144.The stimulation electrodes 188 are also preferably aligned with thelinear channel 174 (note FIG. 9) so that the stimulation electrodes facethe same direction (and the same tissue) as the temperature sensors 170.The location and spacing of the stimulation electrodes 188 on the energytransmission device 126 c is the same as it is on the energytransmission device 128 c. As such, the clamp apparatus 100 c includespairs of stimulation electrodes 188 and 190 (five pairs in theillustrated embodiment) that are aligned with one another and face oneanother, when the clamp apparatus grasps a tissue structure, and arealigned with one another and face one another from opposite sides of thetissue structure. In the illustrated embodiment, two pairs ofstimulation electrodes 188 and 190 are located between the transmittingelectrode 140 and the return electrode 144, two pairs of stimulationelectrodes are located between the transmitting electrode 142 and thereturn electrode, and one pair of stimulation electrodes is locatedbetween the small space between transmitting electrodes and the returnelectrode. The stimulation electrodes 188 and 190 and the coagulationelectrodes 140-144 are also located within a common plane.

There are a number of advantages associated with such an arrangement.For example, the placement of tissue stimulation electrodes 188 and 190on the same surgical device as the tissue coagulation electrodes allowsthe physician to quickly and easily confirm tissue contact and evaluatethe lesion without moving the clamp. Additionally, and as illustrated inFIGS. 31 and 32, the stimulation electrodes 188 and 190 are locatedbetween the energy transmitting portions of the energy transmissiondevices 126 c and 128 c and are also in the current path CP between theenergy transmission devices (which is shown by the dash lines in FIG.31). This arrangement provides more accurate information when thestimulation electrodes 188 and 190 are being used to confirm tissuecontact prior to supplying coagulation energy because the stimulationelectrodes are in contact with the portions of the tissue structurethrough which current will be transmitted, as opposed to being incontact with tissue that is merely close to the current path. Thelocation of the stimulation electrodes 188 and 190 also provides moreaccurate information concerning the lesion itself during and after thetissue coagulation procedure because the stimulation electrodes are indirect contact with the coagulated tissue CT (FIG. 32). The assessmentof the lesion is localized (i.e. the assessment is made directly on thetarget tissue within the current path) and, therefore, facilitateslesion assessment processes that are easier to implement than thosewhich involve stimulating tissue on one side of a lesion and sensingtissue on the other. Here, the assessment is simply whether or notstimulation of the tissue adjacent to the lesion occurs, as opposed toan assessment of the propagation delay between the stimulation pulse onone side of the lesion and the stimulation on the other.

With respect to the specific methods by which tissue contact may beconfirmed after the physician has positioned the energy transmissiondevices 126 c and 128 c on opposite sides of a tissue structure, thestimulation electrodes 188 and 190 may be used to supply pulses ofstimulation energy (sometimes referred to as “pacing” pulses) to thetissue in the current path CP between the energy transmission devices.The stimulation energy will preferably be supplied in bipolar fashion toa single stimulation electrode pair. The physician will then monitor theadjacent tissue, either visually or with a monitor such as an ECG todetermine whether that tissue was stimulated. In the context of thetreatment of atrial fibrillation, for example, the procedure may beperformed after the energy transmission devices 126 c and 128 c areepicardially positioned about one or more of the pulmonary veins. If thestimulation energy stimulates (or “paces”) the adjacent tissue (here,the left atrium), the physician will know that proper contact has beenachieved for the associated portions of the energy transmission devices126 c and 128 c. This process may be sequentially repeated with theother stimulation electrode pairs to insure proper tissue contact withthe other portions of the energy transmission devices 126 c and 128 c.Thereafter, and without moving the electrophysiology clamp apparatus 100c, tissue coagulation energy may be applied to the tissue in the currentpath CP with the electrodes 140-144 to form a lesion.

As noted above, stimulation energy may also be used while the tissuecoagulation energy is being supplied in order to determine when atransmural lesion has been completely formed. Here, stimulation energypulses may be supplied by the electrode pairs to the tissue in thecurrent path CP in the manner described above. The tissue adjacent tothe current path will be monitored, either visually or with an ECG, todetermine when the adjacent tissue is no longer being stimulated. Thesupply of tissue coagulation energy may be discontinued in response tosuch a determination. For example, if the ESU 300 is programmed tosupply coagulation energy for 30 seconds, the supply of energy could endafter 25 seconds if the lesion is completed earlier than wasanticipated, as determined by the inability to stimulate the adjacenttissue. This may be accomplished either manually, or automatically, ifthe ECG is connected to the ESU 300.

It should be noted that tissue becomes non-stimulatable before it isirreversibly coagulated or otherwise irreversibly damaged. Accordingly,tissue coagulation energy should continue to be supplied for a fewseconds after the adjacent tissue ceases to be stimulated by stimulationenergy pulses (i.e. there should be a brief delay before the coagulationenergy is discontinued). It should also be noted that while coagulationenergy is being supplied by the electrodes 140-144, the stimulationenergy should be supplied at a significantly higher amplitude (e.g. 5times higher) than it would be before or after the coagulation procedurebecause tissue that is heated is harder to stimulate. For example, if 4mA pulses are suitable before and after the coagulation procedure, then20 mA pulses should be used during the coagulation procedure.

Finally, stimulation energy may be supplied after tissue coagulationenergy has been discontinued, either at the end of the pre-programmedperiod or based on the sensed completion of the lesion, in order todetermine whether a transmural lesion has been formed. Without movingthe clamp, stimulation energy pulses may be supplied by the electrodepairs to the tissue in the current path CP in the manner describedabove. The adjacent tissue will be monitored, either visually or withthe ECG, to determine whether the adjacent tissue can be stimulated. Ifnot, the physician may assume that a transmural lesion has been formed.In those instances where the lesion is incomplete, the individualstimulation electrode pairs may be used to determine where the gap (i.e.the portion of the lesion that is not transmural) is located. Additionalcoagulation energy may then be supplied as necessary to complete thelesion. Of course, it may be the case that the entire lesion is nottransmural, which would require the coagulation procedure to be at leastpartially repeated.

With respect to sizes and materials, the stimulation electrodes 188 and190 are relatively small (i.e. too small to form transmural myocardiallesions), solid, low profile devices. Suitable surface are sizes areabout 0.2 mm² to 10 mm² , and suitable thicknesses are about 0.01 mm to0.5 mm. The electrodes in the illustrated embodiment are about 1 mm² andabout 0.1 mm thick. Suitable materials include platinum, platinumiridium, stainless steel, gold, silver-silver chloride or othernon-toxic metals. Stimulation electrodes may also be formed by coating aconductive material onto the variable spacing structures 176 or otherunderlying structure using conventional coating techniques or an IBADprocess. Suitable conductive materials include platinum-iridium andgold. An undercoating of nickel, silver or titanium may be applied toimprove adherence. Conductive ink compounds, such as silver-basedflexible adhesive conductive ink (polyurethane binder) or metal-basedadhesive conductive inks (e.g. platinum, gold, or copper based) may alsobe pad printed in place. With respect to assembly, the signal wires 190and 192 may be welded or soldered to solid stimulation electrodes priorto assembly, while coated/printed electrodes may be formed onto the endsof signal wires that are already in place.

Surgical probes may also be provided with stimulation electrodes. Theexemplary surgical probe 200 a illustrated in FIGS. 33-36 is essentiallyidentical to the surgical probe 200 and similar elements are representedby similar reference numerals. Here, however, the distal section 208 aincludes a plurality of the above-described stimulation electrodes 188.The stimulation electrodes 188 are arranged such that a pair ofstimulation electrodes is aligned with each of the seven coagulationelectrodes 210. Signal wires 192, which are connected to the stimulationelectrodes 188 in the manner described above, extend through a cable 240to a connector 242. The handle 206 a includes an aperture 244 for thecable 240.

The surgical probe 200 a may be incorporated into the exemplaryelectrophysiology system 20 a (FIG. 33), which also includes theaforementioned ESU 300, tissue stimulation apparatus 350, and EPrecording apparatus 352. There are a number of advantages associatedwith such as system. Most notably, positioning the tissue stimulationelectrodes 188 on the same surgical device as the tissue coagulationelectrodes 210 allows the physician to quickly and easily confirm tissuecontact and evaluate the lesion without moving the probe. Typically,this will involve providing monopolar stimulation pulses from the pairsof stimulation electrodes 188 that are associated with the coagulationelectrodes 210 that will be forming the lesion.

With respect to tissue contact, and referring to FIG. 37, thestimulation electrode pairs may be used to supply pulses of stimulationenergy to the tissue in the current path CP associated with one of thecoagulation electrodes 210. The physician will then monitor the adjacenttissue in the tissue structure T, either visually or with an ECG, todetermine whether that tissue was stimulated. This process may besequentially repeated with the other stimulation electrode pairs inorder to insure proper tissue contact with the applicable portions ofthe surgical probe distal section 208 a. Thereafter, and without movingthe distal section, tissue coagulation energy may be applied to thetissue in the current path CP with the electrodes 210 to form a lesion.

Turning to FIG. 38, the stimulation electrodes 188 may also be used todetermine lesion depth and, correspondingly, whether or not a lesion istransmural at various points along the length of the lesion. Stimulationenergy may be used to determine lesion depth because non-viable tissue(e.g. coagulated tissue) cannot be stimulated and will not propagatestimulation energy to nearby tissue. As such, when the application ofstimulation energy that should stimulate tissue at a known depth failsto do so, and that depth is greater than or equal to the thickness ofthe body structure, it may be inferred that a transmural lesion has beenformed. Preferably, the stimulation electrodes will be used on acoagulation electrode-by-coagulation electrode basis both during andbefore the coagulation process in the manner described above.

In the context of lesions formed within the heart, for example,localized current densities must exceed about 2 mA/cm² to stimulateheart tissue. With respect to current transmitted from an electrode totissue, the current density is about ½πr², where r is the distance fromthe electrode. Thus, a 1 mA stimulation pulse will typically stimulateviable tissue that is no more than about 2.8 mm from the electrode, a 2mA stimulation pulse will typically stimulate viable tissue that is nomore than about 4.0 mm from the electrode, a 10 mA stimulation pulsewill typically stimulate viable tissue that is no more than about 9.0 mmfrom the electrode, and a 20 mA stimulation pulse will typicallystimulate viable tissue that is no more than about 13.0 mm from theelectrode. The left atrium is, for example, about 3 mm thick andaccordingly, failure to stimulate with a 2 mA stimulation pulseindicates that a transmural lesion has been formed in the vicinity ofthe stimulation electrode. As noted above, these values should besubstantially increased (e.g. by a factor of five) when the stimulationpulses are being supplied at the same time as the coagulation energy.

It should also be noted that there are a number of advantages associatedwith location of the stimulation electrodes 188 relative to thecoagulation electrodes 210. For example, the stimulation electrodes 188are positioned between the coagulation electrodes 210 and target tissue,as opposed to being positioned on the distal section outer member 220between the coagulation electrodes. As such, the stimulation electrodes188 are in the current path of each coagulation electrode 210, asopposed to being in between the current paths the coagulationelectrodes.

Although the inventions disclosed herein have been described in terms ofthe preferred embodiments above, numerous modifications and/or additionsto the above-described preferred embodiments would be readily apparentto one skilled in the art. By way of example, but not limitation, tissuecoagulation assemblies in accordance with the present inventions may beconfigured such that only one of the energy transmission devicesincludes a variable spacing device and/or such that the energytransmission devices are otherwise not identical. It is intended thatthe scope of the present inventions extend to all such modificationsand/or additions and that the scope of the present inventions is limitedsolely by the claims set forth below.

1. An apparatus for use with a clamp including first and second clampmembers, the apparatus comprising: a first energy transmission deviceconfigured to be removably secured to the first clamp member; and asecond energy transmission device configured to be removably secured tothe second clamp member; at least one of the first and second energytransmission devices including a resilient member and a barrier memberformed from different material than the resilient member.
 2. Anapparatus as claimed in claim 1, wherein the first and second energytransmission devices each include a resilient member and a barriermember formed from different material than the resilient member.
 3. Anapparatus as claimed in claim 1, wherein the resilient member isconfigured to retain fluid.
 4. An apparatus as claimed in claim 1,wherein the resilient member comprises a porous member.
 5. An apparatusas claimed in claim 1, wherein the resilient member comprises a foammember.
 6. An apparatus as claimed in claim 1, wherein the barriermember comprises a hydrophilic fabric.
 7. An apparatus as claimed inclaim 1, wherein the barrier member comprises a porous fabric.
 8. Anapparatus as claimed in claim 1, wherein the first and second energytransmission devices each comprise an electrically non-conductivemounting device and an electrode.
 9. A clamp, comprising: first andsecond clamp members, at least one of the first and second clamp membersbeing movable relative to the other of the first and second clampmembers; a first energy transmission element carried by the first clampmember; and a second energy transmission element carried by the secondclamp member; at least a portion of at least one of the first and secondenergy transmission elements being covered by a resilient member and abarrier member formed from different material than the resilient member.10. A clamp as claimed in claim 9, wherein the first and second energytransmission elements are removably secured to the first and secondclamp members.
 11. A clamp as claimed in claim 9, wherein the first andsecond energy transmission elements are both covered by a resilientmember and a barrier member formed from different material than theresilient member.
 12. A clamp as claimed in claim 9, wherein theresilient member is configured to retain fluid.
 13. A clamp as claimedin claim 9, wherein the resilient member comprises a porous member. 14.A clamp as claimed in claim 19, wherein the resilient member comprises afoam member.
 15. A clamp as claimed in claim 9, wherein the barriermember comprises a hydrophilic fabric.
 16. A clamp as claimed in claim9, wherein the barrier member comprises a porous fabric.
 17. A clamp asclaimed in claim 9, wherein the first and second energy transmissiondevices each comprise an electrically non-conductive mounting device andan electrode.
 18. An apparatus for use with a clamp including first andsecond clamp members, the apparatus comprising: a base member configuredto be removably secured to at least one of the first and second clampmembers; at least one energy transmission element carried by the basemember such a portion of the energy transmission element is covered bythe base member and a portion of the energy transmission element is notcovered by the base member; and a variable spacing structure that isconfigured to retain fluid and cover at least part of the uncoveredportion of the energy transmission element and not cover the portion ofthe energy transmission element that is covered by the base member. 19.An apparatus as claimed in claim 18, wherein the variable spacingstructure includes a resilient member.
 20. An apparatus as claimed inclaim 19, wherein the resilient member is configured to retain fluid.21. An apparatus as claimed in claim 19, wherein the resilient membercomprises a porous member.
 22. An apparatus as claimed in claim 19,wherein the resilient member comprises a foam member.
 23. An apparatusas claimed in claim 19, wherein the variable spacing structure includesa barrier member, formed from different material than the resilientmember, over the resilient member.
 24. An apparatus as claimed in claim23, wherein the barrier member comprises a hydrophilic fabric.
 25. Anapparatus as claimed in claim 23, wherein the barrier member comprises aporous fabric.
 26. An apparatus as claimed in claim 18, wherein the atleast one energy transmission element comprises at least one electrode.27. A clamp, comprising: first and second clamp members, at least one ofthe first and second clamp members being movable relative to the otherof the first and second clamp members; a base member carried by at leastone of the first and second clamp members; at least one energytransmission element carried by the base member such a portion of theenergy transmission element is covered by the base member and a portionof the energy transmission element is not covered by the base member;and a variable spacing structure that is configured to retain fluid andcover at least part of the uncovered portion of the energy transmissionelement and not cover the portion of the energy transmission elementthat is covered by the base member.
 28. A clamp as claimed in claim 27,wherein the variable spacing structure includes a resilient member. 29.A clamp as claimed in claim 28, wherein the resilient member isconfigured to retain fluid.
 30. A clamp as claimed in claim 28, whereinthe resilient member comprises a porous member.
 31. A clamp as claimedin claim 28, wherein the resilient member comprises a foam member.
 32. Aclamp as claimed in claim 28, wherein the variable spacing structureincludes a barrier member, formed from different material than theresilient member, over the resilient member.
 33. A clamp as claimed inclaim 32, wherein the barrier member comprises a hydrophilic fabric. 34.A clamp as claimed in claim 32, wherein the barrier member comprises aporous fabric.
 35. A clamp as claimed in claim 27, wherein the at leastone energy transmission element comprises at least one electrode.
 36. Anapparatus for use with a clamp including first and second clamp membersdefining an open orientation and a closed orientation, the apparatuscomprising: first and second energy transmission devices defining firstand second energy transmission surfaces and configured to be removablysecured to the first and second clamp members such that there is aspacing having a predetermined size between the first and second energytransmission surfaces when the clamp is in the closed orientation; andmeans for increasing the spacing between the first and second energytransmission surfaces when the first and second energy transmissionsurfaces are brought into contact with a tissue structure that isthicker than the predetermined spacing size.
 37. A clamp, comprising:first and second clamp members, at least one of the first and secondclamp members being movable relative to the other of the first andsecond clamp members between an open orientation and a closedorientation; first and second energy transmission devices defining firstand second energy transmission surfaces and configured to be removablysecured to the first and second clamp members such that there is aspacing having a predetermined size between the first and second energytransmission surfaces when the clamp is in the closed orientation; andmeans for increasing the spacing between the first and second energytransmission surfaces when the first and second energy transmissionsurfaces are brought into contact with a tissue structure that isthicker than the predetermined spacing size.